1. Technical Field
The present invention relates generally to cryptographic communications, and more particularly, to a system and method for simplifying the addressing of public key-encrypted communications.
2. Description of Background Art
In symmetric key cryptography, both the sender and receiver of a message use the same secret key. The sender uses the secret key to encrypt the message and the receiver uses the same secret key to decrypt the message. However, a difficulty arises when the sender and receiver attempt to agree on the secret key without anyone else finding out. For example, if the sender and receiver are in separate physical locations, they must trust a courier, a telephone system, or some other transmission medium to prevent the disclosure of the secret key. Anyone who overhears or intercepts the key in transit can later read, modify, and forge all messages encrypted or authenticated with that key. Thus, symmetric key encryption systems present a difficult problem of key management.
Public key cryptography was developed as a solution to the key management problem. In public key cryptography, two keys are used—a public key and a private key. The public key is published, while the private key is kept secret. Although the public and private keys are mathematically related, neither can be feasibly derived from the other.
To send a private message using public key cryptography, a message is encrypted using the recipient's public key, which is freely available, and decrypted using recipient's private key, which only the recipient knows. Thus, the need for the sender and recipient to share secret information is eliminated. A sender only needs to know the recipient's public key, and no private keys are ever transmitted or shared.
Public key cryptography has another advantage over symmetric key cryptography in the ability to create digital signatures. One of the significant problems in cryptography is determining whether an encrypted message was forged or modified during transmission. As noted above, if a symmetric key is lost or stolen, any person in possession of the key can create forged messages or modify legitimate messages.
Using public key cryptography, however, a sender can digitally “sign” a message using the sender's private key. Thereafter, the recipient uses the sender's public key to verify that the message was actually sent by the sender and was not modified during transmission. Thus, a recipient can be confident that a message was actually sent by a particular sender and was not modified during transmission.
Despite its many advantages, public key cryptography presents three basic difficulties. First, in order to send private messages, the sender must know beforehand the public key of the recipient. Conventional public key systems typically rely on a sender's locally-maintained address book of public keys. Thus, if the recipient's public key is not in the sender's address book, the sender must somehow contact the recipient by telephone or e-mail, for example, to request the recipient's public key. Such systems are cumbersome and inconvenient, and prevent widespread adoption and use of public key cryptography.
More fundamentally, another problem with public key cryptography is that a recipient must first have a public key in order to receive an encrypted message. Because the technology is relatively new, only a few users have currently obtained public keys. This fact, alone, represents a significant barrier to adoption because a sender cannot encrypt a message to the recipient until the recipient has completed the process of obtaining a public key.
Yet another problem with public key cryptography is the relatively ease for “spoofing” a public key. In other words, a first user may publish his public key in the name of a second user and thereby receive private communications intended for the second user. Various solutions, such as digital certificates and certificate authorities (CA's), have been proposed to address this problem, but are not relevant to present application.
Accordingly, what is needed is a system and method for securely transmitting an information package using public key cryptography in which the sender is not required to know the recipient's public key before the package is sent. Indeed, what is needed is a system and method for securely transmitting an information package using public key cryptography in which the recipient is not required to have a public key before the package is sent.